This invention relates to controlling the density of bales produced in an extrusion-type baler wherein successive charges of material are introduced into a baling chamber and are forced through a restricted orifice by a reciprocating plunger. Typical prior control systems for this class of baler have relied upon mechanical sensors which activate a separate hydraulic control circuit for squeeze cylinders that control the size of the orifice. Such sensors normally activate the circuits to either relieve or add fluid pressure depending upon the extent to which the sensors can penetrate the forming bale. In other words, the "tightness" or density of the forming bale results in the sensor being physically positioned in such a way that it performs an appropriate valving function so as to either further pressurize or depressurize the squeeze cylinders.
However, systems of this type rely upon very localized "readings" of bale density and thus may not accurately reflect the overall or average density of the bale being formed. Hence, the degree of uniformity of density throughout the bale may suffer.
Rather than sense bale density on a local, concentrated basis in the foregoing manner, the present invention contemplates sensing pressure build-up in the hydraulic circuit that controls the squeeze cylinders and takes such corrective steps as may be necessary in response to that build-up, such being possible as a way to provide the necessary control function inasmuch as the pressure build-up in the circuit is directly related to the resistance encountered by the bale as it attempts to move through the orifice under the impetus of the plunger. Thus, by basing the control system on resistance to bale movement rather than depth of penetration at any localized spot in the bale, the condition of the bale as a whole is more fully considered, to the end that adjustments which more accurately reflect the state of things can be automatically effected.
While the concept of utilizing the perception of hydraulic pressure to trigger a certain control function in a baler is not per se new, prior systems attempting to incorporate such an approach have suffered from the disadvantage of being undeuly complex and unreliable. Accordingly, one important object of the present invention is to provide a simplified system wherein a single cylinder provides the dual function of sensing the compaction force on the plunger and also acting as a pump to supply the necessary pressurized fluid to actuate the squeeze cylinders controlling the orifice.
Another important object of the present invention is to provide a fluid-pressure-triggered system as aforesaid, which is based on the principle that more nearly uniform bale density can be achieved if the system is geared toward keeping the plunger operating at a certain constant compactive force regardless of variations in crop conditions such as, for example, moisture content and the coefficient of friction between the crop and walls of the baling chamber. Inasmuch as variables of this type can and do affect the pressure level at the squeeze cylinders that is required in order to arrive at a certain constant force loading on the plunger, it is important to have a system that will accommodate such pressure fluctuations at the squeeze cylinders without causing a responsive adjustment in the system that would increase or decrease the compactive force of the plunger.
Stated differently, it is recognized that certain crop conditions may require one pressure level at the squeeze cylinders to achieve a certain amount of compactive force by the plunger while a second crop condition may require a different pressure level at the squeeze cylinders to achieve the same compactive force at the plunger. For example, straw may be easier to push through the bale chamber than hay because of straw's "slickness" and may thus require greater pressure at the squeeze cylinders in order to achieve the same compactive force from the plunger as with hay. Accordingly, if the system is to be based upon the proposition that more uniformity of bale density can be ultimately achieved if the system is geared to maintaining a certain constant compactive force of the plunger, then it is desirable to have a system that will achieve such end notwithstanding the fact that it may take different squeeze pressures at different times to produce that certain compactive force from the plunger.
Hence, it is an important object of this invention to provide a fluid-pressure-triggered system which is capable of operating at a relatively constant compactive plunger force while tolerating wide fluctuations in pressure levels at the squeeze cylinders.
An additional important object of this invention is to mechanically link the plunger with the hydraulic pump of the system in such a way that the resistance encountered by the plunger during its compaction stroke is transmitted to the pump so as to displace the latter through a pumping stroke, thus adding a charge of pressurized fluid to the hydraulic circuit that can be routed to the squeeze cylinders if additional pressure is required at that location to bring the compactive force of the plunger up to its desired level.
Additionally, an important object of this invention is to provide an arrangement wherein increases or reductions in the pressure level of the squeeze cylinders are made in relatively small increments so as to avoid the possibility of sudden drastic pressure drops or increases that would adversely affect bale density.
Yet another important object of this invention is to provide a way in which the compactive force for the plunger can be selected or adjusted as may be necessary and desirable.
A further object of this invention is to void the requirement for an independent pump source for actuating the squeeze cylinders.
The invention will be more readily understood when the following description of certain embodiments are described in detail in conjunction with the drawing illustrating the invention in schematic form.